Control valves typically include a valve plug that is movable toward and away from a valve seat formed in a valve port between a fluid inlet and a fluid outlet. The movement of the valve plug is typically controlled by an actuator. The problem with existing valves is that hydraulic effects are placed on the plug due to pressure differentials in the valve. As a result, larger actuators are required to open or close the valve plug.
FIG. 1 shows a conventional two-seated balanced valve. Valve body 10 as shown in FIG. 1 comprises a pair of seat rings 15, 20 to accommodate a pair of valves plugs 25 and 30 to control the flow of liquid between inlet port 35 and outlet port 40. Valve stem 45, which is connected to an actuator, not shown, is provided to control the position of the valve plugs 25 and 30. Valve 10 is further provided with pressure chambers 50 and 55 are provided to balance the pressure of valve plugs 25 and 30 due to the pressure created on the valve plugs as fluid progresses through valve 10 between inlet port 35 and outlet port 40. The problem with such an arrangement is that in order to minimize leakage, the distance between the valve plugs 25 and 30 and the seat rings 15 and 20 needs to be nearly identical, which is difficult to accomplish. Accordingly, such as balanced valve design is generally given a lower leakage classification. What is needed is a balanced valve design without the leakage problems associated with prior balanced valve designs. Accordingly, there is currently a need to balance the differential pressures in the valve to permit operation of such valves in highest differential pressure applications than is possible with conventional valve and actuator combinations.